Optical discs such as compact discs (CD's), digital video discs (DVD's), laser discs and the like are widely used in the computer and consumer electronics industries as a relatively inexpensive and reliable medium for storing audio, video and/or other digital information. Optical discs may be produced from relatively inexpensive media and are readily suited for mass production.
A wide variety of manufacturing processes performed during the production of optical discs are tailored for processing tens or hundreds of optical discs at a time. To simplify the performance of these processes on automated equipment, as well as to facilitate the transfer of optical discs between various processes, the optical discs are often stacked together on a "spindle" having a shaft that extends through the central aperture in each optical disc. A number of manufacturing processes rely on optical disc spindles, including but not limited to molding, reflecting, protecting, printing, and packaging, among others.
One difficulty associated with the use of such optical disc spindles is that a spindle from time to time may become "bent", where the shaft is no longer perpendicular to the base of the spindle. It has been found that if a spindle is bent beyond a certain amount, problems can arise with the automated equipment with which the spindle is used, often resulting in defective discs and/or equipment failures. Often, this amount is relatively small (e.g., less than a 1 mm deflection at the free end of the shaft), so visual detection by an operator is usually not feasible. Often, a bent spindle is not detected until equipment fails or defective discs are produced. In either event, manufacturing costs often increase and productivity often decreases.
Manual methods of testing the straightness of an optical disc often require a technician to manually take multiple measurements at various points on a spindle. Such manual methods are often time consuming and unreliable due to measurement errors.
Therefore, a substantial need has arisen for a manner of quickly and reliably detecting the straightness of optical disc spindles used in the production of optical discs and the like.